Method and device for controlling a plurality of relay nozzles in a jet weaving machine

ABSTRACT

Method of controlling a plurality of relay nozzles (RNx) is a jet weaving machine. These nozzles are consecutively actuated for supporting the insertion of the weft yarn (WY) into the shed of the weaving machine and up to the arrival end (AE) of said shed by means of consecutively opening solenoid valve associated with nozzles. The valves are controlled on the basis of calculated information representing the momentary real position of the weft yarn (WY) during it path in the shed. The invention also relates to an apparatus for carrying out said method.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for controllinga plurality of relay nozzles in a jet weaving machine.

BACKGROUND OF THE INVENTION

The present invention relates to a method and device for controlling aplurality of relay nozzles in a jet weaving machine. Such relay nozzlesare sequentially actuated, i.e. opened, for supporting the insertion ofthe weft yarn into the shed of the weaving machine, from the insertionside of the machine and up to the arrival end of the shed on the otherside of the machine. The actuation of the relay nozlzes is carried outby sequentially opening electro-magnetic or solenoid valves associatedwith the nozzles. In some known types of weaving machines the relaynozzles are kept open from the moment when they are opened up to themoment when the weft yarn reaches the arrival end of the shed, at whichlatter moment all relay nozzles are closed simultaneously. In othertypes of machines the relay nozzles are sequentially closed apredetermined moment of time after they have been opened. The presentinvention is applicable to both these different kinds of relay nozzlecontrol.

A known method of the above-mentioned kind is for example disclosed inGerman Offenlegungsschrift No. 28 36 206. There, the relay nozzles areactuated in synchronism with the rotation of the main shaft of theweaving machine. For carrying out this known method, theelectro-magnetic or solenoid valves associated with the relay nozzlesare connected to and thus receive actuation signals from a rotary sensorin the form of a code disc co-acting with an optical detector, said codedisc being fixed on the main shaft.

This known method works in an optimal way only if there is a perfectsynchronism between the weft insertion process and the rotation of themain shaft of the weaving machine. However, such a synchronism cannotalways be maintained, since on one hand the main shaft rotation is arelatively non-varying parameter in this connection, whereas on theother hand the weft yarn insertion curve as a function of time can varya great deal in dependence on e.g. the pressure of the utilizedcompressed medium, preferably air, and also from yarn to yarn havingdifferent friction coefficient, thickness and structure. This means withthe known method that the control of the nozzles must be carried outwith sufficient compensation for the variations in synchronism betweenthe weft insertion process and the main shaft rotation, preferably byproviding relatively generous time tolerances for the sequential opening(and closing, if any) of the series of nozzles. As a consequence hereofthe nozzles will consume much more pressure medium (air) than would benecessary for the support of weft insertion as such, which altogethermeans higher production costs for the woven fabric.

The object of the present invention is primarily to provide a method anda device by which the above-mentioned drawbacks have been eliminated.

SUMMARY OF THE INVENTION

This is achieved in accordance with the invention by the solenoid valvesfor the relay nozzles being controlled on the basis of calculatedinformation representing the momentary actual position of the leadingend of the weft yarn during its path in the shed of the weaving machine.

By this method the necessary opening time intervals can always,irrespective of varying compressed medium pressure, wearing of thenozzles and valves, and utilized yarn quality, be kept at a minimum,which means considerable savings in compressed medium consumption andcorresponding reduction of production costs.

An apparatus for carrying out this new method is based on Applicant'sown earlier international patent application No. PCT/EP 83/00254 and hasa yarn storing, feeding and measuring device for the weft yarn to besupplied into the shed of the weaving machine, said device comprising astationary storing drum onto which an intermediate yarn store is woundby a winding-on member and from which the yarn is withdrawn spirallingaround the withdrawal end of the storing drum. Said device alsocomprises yarn sensing means being arranged such that the yarn ispassing its detection area during withdrawal from the drum, said yarnsensing means producing pulse signals, each pulse indicating that theyarn passes its detection area, a plurality of yarn stopping devicesbeing arranged at angular intervals around the storing drum, said yarnstopping devices consisting of yarn stopping elements and of actuatormeans for moving said stopping elements into and out of the path of theyarn being withdrawn, and an actuator control device adjustable todesired yarn lengths to be withdrawn and comprising storing means forstoring information regarding the yarn stopping device actuated at theend of a previous yarn withdrawal cycle. In accordance with the presentinvention the actuator control device comprises calculating means fordetermining the momentary position of the withdrawal point of the yarn,based on said stored information and of the period of time between twosubsequent pulse signals from the yarn sensing means, which calculatingmeans is electrically connected to the solenoid valves of the relaynozzles, and the calculating means transmits on actuation signal to eachrespective one of said nozzles for opening said nozzle at the momentwhen the calculated momentary position of the withdrawal point of theyarn on the storing drum corresponds to a yarn length being withdrawnwhich equals the distance of said nozzle from the yarn insertion end ofthe shed of the weaving machine.

In the preferred embodiment of the present invention the calculatingmeans is also arranged to transmit a de-actuation signal to eachrespective nozzle for closing same a predetermined moment of time afterits opening, preferably at the moment when the calculating meanstransmits an actuation signal to the subsequent nozzle in the seriesalong the shed of the weaving machine.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be describedwith reference to the enclosed drawings, where

FIG. 1 schematically shows an embodiment of the weft insertion means ofa jet weaving machine, known per se, in which the method in accordancewith the present invention can be carried out, and in which a deviceaccording to the invention is comprised as one of the components;

FIG. 2 shows a side view of a device by which the method in accordancewith the invention can be carried out, partially in cut- andcross-sectional representation;

FIG. 3 shows a front view of the device as shown in FIG. 2;

FIG. 4 shows, as well as FIG. 5, details of the device shown in FIGS. 2and 3;

FIG. 6 shows a circuit diagram of a control unit comprised in the deviceshown in FIGS. 2-5;

FIG. 7 shows a flow diagram used in a microprocessor of the control unitas shown in FIG. 6.

DETAILED DESCRIPTION

In FIG. 1, the weft insertion means for the weft yarn WY in a jetweaving machine, of conventional kind per se, here a so called air jetloom, comprises a main air jet nozzle MN and a number of so called airjet relay nozzles, by way of example let us say sixteen nozzles, ofwhich here only six are shown RN1-RN6. All nozzles are supplied withcompressed air via conduits CMN and C1-C6 from a compressed air sourceCAS, preferably a conventional air compressor. The supply of compressedair to the nozzles is controlled by means of solenoid valves VMN, V1-V6,which in turn are electrically connected to and controlled by means of acentral control electronic unit CCU, which will be described in detailin the following with reference to FIGS. 6 and 7.

The weft yarn WY comes from a yarn spool YS and is wound onto a yarnstoring, feeding and measuring device MD in accordance with theinvention, which will be described closely in the following withreference to FIGS. 2-5. This yarn storing, feeding and measuring deviceis also connected to and controlled by the central control electronicunit CCU.

The weft yarn WY is withdrawn from the yarn storing, feeding andmeasuring device MD and is inserted into the weaving shed WS of theweaving machine by the main air jet nozzle MN being actuated when valveVMN is opened due to an actuation signal from the central control unitCCU. The further insertion of the weft yarn WY into the shed and over tothe so called arrival end AE thereof is supported by sequentially, in aconsecutive manner, actuating the sixteen relay nozzles RN1-RN16, theactuation of each respective nozzle being controlled from the centralcontrol unit CCU by the method according to this invention, which willbe described in detail further below.

Referring now to FIG. 2, a feeding device 1 consists of a storage drum2, a winding-on device which is an orbiting feeder tube 3 and anelectric motor 4. A weft yarn WY being supplied to the orbiting feedertube 3 driven by the electric motor 4 is wound onto the storage drum 2.This storage drum is a stationary storage drum being maintained in astationary position with respect to its environment by a magnetic means(not shown here, but well-known in the art). Devices of this type arefor example shown in U.S. Pat. Nos. 3 776 480 and 3,843,153. The feedingdevice 1 is provided with a yarn store sensor 5 located close to thegenerally cylindrical surface of the storage drum 2. This store sensor 5can be a so called maximum sensor preferably consisting of a lightemitting device and a light sensing device. The yarn store sensor 5generates a signal indicating the amount of yarn stored on the drum,i.e. in principle the number of turns of yarn wound onto the drum. Basedon this signal, a store control unit 7 controls the operation of theelectric motor 4 in such a way that there is continuously a sufficientamount of yarn available on the yarn storage drum 2. Yarn store controlunits are per se known in the art. For purposes of the presentdisclosure, it should be noted that this art is exemplified by GermanOffenlegungsschrift No. 29 08 743, French Publication No. 1 562 223 andInternational application Ser. No. PCT/EP 83/00121 (applicant's own)which corresponds to U.S. Ser. No. 588,866 filed Jan. 10, 1984.

As shown in FIG. 2, there is disposed a yarn sensing means 6 at thewithdrawal end of the storage drum arranged such that the yarn ispassing its detection area during withdrawal from the drum 2. This yarnsensing means preferably consists of a single yarn sensor 6 producingpulse signals, each pulse signal indicating that the yarn WY passes thedetection area of the sensor 6. This sensor 6 could also be located infront of the withdrawal end of the storage drum, but has to be arrangedsuch that the yarn is passing its detection area during withdrawal fromthe storage drum 2. A yarn stopping device 10 located at the withdrawalend of the storage drum 2 consists of an actuator means comprising aplurality of electromagnetic coils 11 being wound around a coil core 12supoorted by a balloon limiting ring 13 consisting of two U-shaped ringscovering said plurality of electromagnetic coils 11. Said balloonlimiting ring 13 is fixedly secured to the stationary part of thefeeding device 1, for example to a base plate thereof. A ringshapedguiding portion 16 is connected to the withdrawal end of the storagedrum 2. Said guiding portion 16 supports a plurality of yarn stoppingelements, each of said yarn stopping elements consisting of a metal ball14 being movably disposed in a radial bore 15 provided in the guidingportion 16.

As shown in FIGS. 4 and 5, the respective electromagnetic coils 11 andassociated cores 12 are arranged opposite to said bores 15. The balloonlimiting ring 13 and the guiding portion 16 define a gap 18 which ispreferably in the order of 1-2 millimeters. The yarn WY passes said gapwhen being withdrawn from the storage drum 2. A permanent magnet 17 islocated at one end of each bore 15 for moving back said metal ball 14into said bore 15 after switching off an actuation current fed to therespective electromagnetic coils 11. As shown in FIGS. 4 and 5, themetal ball 14 is attracted by the magnetic force of the coil 11 whenswitching on the actuation current fed to the coil 11. The width of thegap 18 corresponds to the radius of the metal ball 14. When the coil 11is not actuated, the permanent magnet 17 will attract the metal ball 14,so that the ball will be completely positioned inside the bore 15,whereby the yarn WY can be freely withdrawn in the axial direction fromthe storage drum 2.

The magnetic force of each electromagnetic coil 11 is chosen such thatthis force will overcome the attraction force of the permanent magnet 17when feeding the actuation current to the coil 11. The metal ball 14will thereby move outwardly in the radial direction of the bore 15 andcome into contact with the free end of the coil core 12. In thiscondition, approximately half the metal ball locks the gap 18 for thepassage of the yarn WY in such a way that the withdrawal of the yarnfrom the storage drum 2 is terminated. When switching off the actuationcurrent fed to the coil 11, the tension in the yarn WY, being pulled atthe beginning of the weft yard insertion into the weaving machine,co-acts with the magnetic force of the permanent magnet 17 such that themetal ball 14 will return to its starting position so as to come intocontact with the permanent magnet 17. As the tension of the yarn co-actswith the magnetic force of the permanent magnet 17 due to the shape ofthe metal ball 14, the holding force of the permanent magnet 17 can berelatively low. Hence, only a small portion of the attracting forcegenerated by the electromagnetic coil 11 is required for overcoming themagnetic force of the permanent magnet 17. For this reason, the yarnstopping device 10 works faster than prior art devices using stoppingelements which are needle-shaped or pin-shaped. For further enhancingthe operation of the yarn stopping device 10, a thin plate ofnon-magnetic material can be positioned at the outer end of thepermanent magnet 17 and/or on the free end of the coil core 12 foreliminating a magnetic sticking or "adhesion" between the metal ball 14and permanent magnet 17 and/or the coil core 12.

The stopping element 14 can also have the form of a shortcylindrical pinwith a plane inner end directed to the permanent magnet 17 and arounded, preferably semi-spherical end.

Referring now to FIG. 6, the control device CCU will be hereinafterdescribed in detail. The control device comprises a calculating means20, which is a standard microprocessor. The microprocessor 20 ispreferably a microprocessor of the type 8748, manufactured by the INTELCorp., U.S.A. The yarn sensor 6 is connected to an input 21 of a yarnsensor interface circuit 22. The yarn sensor interface circuit 22essentially consists of an operational amplifier 23 connected, through adiode 24 and a resistor 25 connected in parallel to diode 24, to aninverter gate 26, the output thereof being connected to input pin INT ofthe microprocessor 20. The input terminals of the inverter gate 26 areconnected to ground via a capacitor 27. The gain of the operationalamplifier 23 can be adjusted by a variable gain control resistor 28connected to the operational amplifier 23. When a pulse is generated bythe yarn sensor 6, it will be current-amplified by the operationalamplifier 23. The output current of the operational amplifier 23 passesthe diode 24 and charges the capacitor 27. When the pulse signal goesback to zero potential, the capacitor 27 is discharged through resistors25, 29 and 30 to ground. Due to the switching threshold of the invertergate 26, only pulses of a predetermined voltage are detected, so thatthe yarn sensor interface circuit 22 disregards small noise voltages. Asthe capacitor can be quickly charged through diode 24 and is only slowlydischarged through resistors 25, 29 and 30, short input pulses aretransformed to longer output pulses as generated by gate 26. Such abroadening of the very short input pulses enables the microprocessor 20to reliably detect the input pulses, i.e. the extremely quick passagesof the yarn in the detection area of the sensor 6.

The microprocessor 20 is supplied with sync signals generated by acrystal resonator 31 connected to input pins XTAL of the microprocessor.

A trigg-input 32 receives a signal picked up at the main shaft of theweaving machine. This signal is applied to the input of anopto-electronical coupling element 33, the output of which is connectedto pin TO of the micro-processor. The trigg-signal serves to synchronizethe operation of the loom with the operation of the microprocessor 20controlling the yarn storing, feeding and measuring device 1. Moreparticularly, the occurrence of the trigg-signal indicates that the nextweft yarn insertion cycle is about to start.

In the central control unit CCU there is provided a combined number ofnozzles/yarn length setting switching device, preferably consisting ofthree BCD-switches 34-36 and a Hexadecimal code switch 27, each of theseswitches having four input terminals and one output terminal. Each ofthe BCD-switches can be set to a decimal number from 0-9 and theHexadecimal code switch from 0-F (=16). This decimal or hexadecimalnumber is converted by the respective switch such that the correspondingone of its four input terminals is connected to its output terminal inaccordance with the code. When for example setting one of theBCD-switches to the decimal number 5, then its first and third inputterminals are connected to its output terminal, whereas its second andfourth input terminals are disconnected from the output terminal. Therespective first input terminals of the switches 34-37 are connected viadiodes to input pin D83 of the microprocessor 20, the respective secondinput terminals of the switches are connected via diodes to input pinD82 of the microprocessor, the respective third input terminals of theswitches are connected via diodes to input DB1 of the microprocessor andthe respective fourth input terminals of the switches are connected viadiodes to input DB0 of the microprocessor 20. The respective outputterminals of the switches 34-37 are connected to output pins P40-P43 ofan expansion circuit 38, here a standard circuit INTEL 8243, the fourinput pins of which are connected to output pins P20-P23 of themicroprocessor 20. At the beginning, each of the input pins DB0-DB3 ofthe microprocessor 20 is in its "high" state, i.e. logical onepotential. The input pins P20-P23 of the microprocessor are also in the"high" state. For reading the value of one of the switches 34-37, themicroprocessor 20 pulls down the voltage of one of its input pinsP20-P23. For example, for reading the BCD value of BCD switch 34, themicroprocessor will generate a predetermined combination of "high" and"low" potential pins on its pins P20-P23 and PROG, whereby pin P40 ofcircuit 38 will receive "low" potential. In case the decimal numberselected by switch 34 is "5" the voltage of input pins DB3 and DB1 ofthe microprocessor 20 will be pulled down to zero potential, i.e. to the"low" logical state, whereas the logical state of input pins DB2 and DB0remain "high".

Output pins P10-P17 of the microprocessor 20 are connected to input pins1-8 of an amplifier circuit 39, this amplifier circuit or driver circuit39 having eight output terminal pins 11-18, each of these beingassociated with a respective input pin 1-8. When receiving an inputsignal of "high" potential (logical one) at its input pins 1-8, theamplifier circuit 39 connects the corresponding output terminal pin to avoltage source having a potential of -35 Volts. Each of the output pins11-18 of the amplifier circuit 39 is connected to three electromagneticcoils 11. Twenty-four electromagnetic coils 11 associated withtwenty-four yarn stopping devices 10 are arranged as a matrix havingeight rows and three columns. The respective output terminals of theelectromagnetic coils 11 arranged in one column are connected to arespective one of three output conductors 40-42.

Output pins P24-P26 of the microprocessor 20 are connected throughcurrent amplifier circuits 43-45 to input pins 1-3 of a further drivercircuit 46. This driver circuit 46 includes three three output pins14-16, each being connected to a respective one of the conductors 40-42.When receiving a "high" potential (logical one) at one of its inputpins, the driver circuit 46 connects the corresponding output pin to avoltage of +5 Volts. Due to the above described circuit matrixarrangement, the microprocessor 20 is enabled to energize one of thetwenty-four electromagnetic coils 11 by generating a high potential atone of the output pins P10-P17 determining the row of the coil 11 to beactuated, and by generating a high potential at one of its output pinsP24-P26 selecting the column of the electromagnetic coil 11 to beactuated. The above described matrix arrangement allows actuation of oneelectromagnetic coil 11 among the twenty-four electromagnetic coils 11with only eleven output pins P10-P17 and P24-P26.

Output pin P27 of the microprocessor 20 is connected to the input pin CSof the first expansion circuit 38 as well as to a corresponding inputpin CS of a second expansion circuit 47, this also being a standardcircuit INTEL type 8243, through over an inverter 48. Output pin P51 ofthe first expansion circuit 38 is connected via a current amplifier 49to a light-emitting element 50, which in turn is connected to ground viaa resistor 51. The light-emitting element 50 actuates an opto-sensitiveswitching element 52 actuating a stop-motion-relay (not shown here) ofthe weaving machine.

Output pin P50 of the first expansion circuit 38 is connected throughthe driver circuit or current amplifier 49 to a relay of the valve VMNof the main air jet nozzle MN of the loom (shown in FIG. 1).

The amplifier circuits 39 and 49 are standard circuit elements of thetype UDN 2580A. The amplifier or driver circuit 46 is also a standardcircuit element of the type UDN 2002. The manufacturer of all thementioned driver or amplifier circuits is the SPRAGUE Corp. U.S.A.

Output pins P40-P43, P50-P53, P60-P63 and P70-P73 of the secondexpansion circuit 47 are each connected via one of two amplifier ordriver circuits 53 or 54, in the form of standard circuit elements typeUDN 2580A, to a respective relay in the solenoid valve of one of thesixteen relay nozzles RN1-RN16 along the path of the weft yarn in theshed of the weaving machine.

The two expansion circuits 38 and 47 receive instruction signals totheir input pins PROG from the PROG output of the microprocessor 20.

Referring now to FIG. 7, there is shown a flow diagram of the controlprogramme stored in the read-only memory of the microprocessor 20. Whenreceiving a reset signal, the microprocessor 20 is reset so as to startthe carrying out of the programme with the first instruction thereof,being the "START" instruction.

At programme step No. 1, the microprocessor 20 actuates a predeterminedyarn stopping device 10 for locking the yarn WY in its start position.Preferably, said stopping device 10 is selected such that its angularposition is 180° off-set with respect to the angular position of theyarn sensor 6. The microprocessor 20 stores the number or the angularposition of said stopping device in a predetermined storage cell of itsRAM.

At programme step No. 2, the microprocessor 20 consecutively reads theBCD code of the switches representing the desired weft yarn length andstores the corresponding BCD codes in predetermined storage cells of itsRAM.

At programme step No. 3, the microprocessor 20 converts the BCD codesrepresenting the desired weft yarn length to a digital valuecorresponding to the number of full revolutions and 1/24 revolutions ofthe storage drum, whereby this digital value represents the number ofrevolutions which the withdrawal point of the yarn travels duringwithdrawal of the desired weft yarn length. It is also possible toexpress said desired weft yarn length by a value corresponding to thetime required for withdrawing said desired weft yarn length.

At programme step No. 4, the microprocessor 20 reads the hexa-decimalcode of the switch 37 representing the actual number of relay nozzles ofthe weaving machine in question, i.e. in this case F=16.

At programme step No. 5, the microprocessor 20 calculates the distancebetween the relay nozzles on the basis of the set weft yarn length,since in this embodiment the relay nozzles are positioned with equalinterspacings along the whole shed of the weaving machine.

At programme step No. 6, there is a waiting routine, causing themicroprocessor 20 to await the receipt of a trigg-signal from theweaving machine before going further to programme step No. 7. Thiswaiting routine is realized by a programme loop periodically checkingwhether the trigg-signal occurs. If said condition is fulfilled, themicroprocessor continues with the programme step No. 7.

At programme step No. 7, the microprocessor generates a "high" potentialat its output pin P50 for actuating the relay controlling the valve ofthe main air jet nozzle in the weaving machine.

At programme step No. 8, tne stopping device 10 actuated duringprogramme step No. 1 is deactuated for releasing the yarn WY.

At programme step No. 9, the microprocessor 20 checks whether the yarnpasses the yarn sensor 6 by repeatedly checking the logical state on itsinput pins P1 and P6. If this condition is fulfilled, the microprocessor20 continues with proramme step No. 10.

At programme step No. 10, the microprocessor 20 starts to measure thetime lapsing from the moment of generation of the pulse signalindicating the passage of the yarn through the detection area of theyarn sensor 6.

At programme step No. 11, the microprocessor 20 again carries out awaiting loop corresponding to the waiting loop of programme step No. 6.As soon as the yarn has passed the yarn sensor 6, microprocessor 20continues with the programme step No. 12.

At programme step No. 12, the microprocessor 20 stores the time betweentwo subsequent pulse signals as received from the yarn sensor 6. Themicroprocessor 20 then starts again to measure the time.

At programme step No. 13, the microprocessor 20 calculates at which yarnwithdrawal position the main air jet nozzle is to be switched off.

At programme step No. 14, the microprocessor 20 calculates at which yarnwithdrawal position the stopping device 10 determined during programmestep No. 3 is to be actuated.

At programme step No. 15, the microprocessor 20 calculates the momentaryposition of the yarn withdrawal point on the storage drum based on theactual yarn withdrawal speed being measured during programme step No.12.

At programme step No. 16, the microprocessor 20 checks whether thecalculated, momentary position of the yarn withdrawal point asdetermined during programme step No. 15 corresponds to the position ofthe next relay nozzle RN in the shed, which means that the leading endof the weft yarn WY has reached the position of the next relay nozzleduring its insertion in the shed of the weaving machine. If thiscondition is fulfilled, the microprocessor 20 continues with programmestep No. 17. If not, it continues with programme step No. 18. Of course,this means that when this programme step No. 16 is carried out for thefirst time after start of the yarn withdrawal the microprocessor 20checks if the calculated, momentary position of the yarn withdrawalpoint corresponds to the position of the first relay nozzle RN1, whereaswhen this programme step No. 16 is carried out for the second time aftera yarn withdrawal start, the microprocessor 20 will compare thecalculated, momentary position of the yarn withdrawal point with theposition of the second relay nozzle RN2, and so on.

In this embodiment of the invention, at programme step No. 17, themicroprocesor 20 will open the "next" relay nozzle RN in the series andclose the next preceding relay nozzle by appropriately generating a"high" potential or a "low" potential on the respective output pins11-18 belonging to the nozzles in question of the driver circuits 53,54.

In another possible embodiment of the invention, at programme step No.17, the microprocessor 20 will only open the "next" relay nozzle in theseries, whereas the closing of all relay nozzles is arranged to takeplace simultaneously with the closing of the main jet nozzle, i.e. atthe end of the weft insertion process.

At programme step No. 18, the microprocessor 20 checks whether thecalculated, momentary position of the yarn withdrawal point asdetermined during programme step No. 15 equal to the position determinedduring programme step No. 13. If this condition is fulfilled, themicroprocessor 20 continues with programme step No. 19. If not, itcontinues with programme step No. 20.

At programme step No. 19, the microprocessor 20 switches off the mainjet nozzle MN by pulling down the output pin P50 of the first expansioncircuit 38.

At programme step No. 20, the microprocessor 20 checks whether thecalculated, momentary position of the yarn withdrawal point asdetermined during programme step No. 15 corresponds to the yarn positionas calculated during programme step No. 14. If so, the microprocessorgoes to programme step No. 27. If not, it continues with carrying outprogramme step No. 21.

At programme step No. 21, the microprocessor 20 checks if the calculatedposition as determined during programme step No. 15 is close to theposition of the yarn sensor 6. By doing so, a time-window is realized.In case this condition is not fulfilled, the microprocessor 20 goes backto programme step No. 15. If it is fulfilled, it continues withprogramme step No. 22.

At programme step No. 22, the microprocessor 20 again checks if the yarnhas passed the yarn sensor 6. This programme step corresponds toprogramme step No. 9. If this condition is fulfilled, the microprocessor20 continues with programme step No. 23. If not, it continues withprogramme step No. 24.

At programme step No. 23, the microprocessor 20 stores the measured timebetween two subsequent pulse signals as received from the yarn sensor 6and goes back to programme step No. 15.

At programme step No. 24, there is a safety-routine for checking if ayarn breakage has occurred. This safety-routine is realized by comparingthe calculated time with a time threshold which is only exceeded in caseof a yarn breakage. In other words, the microprocessor 20 checks whetherthe measured time lapsed since the last passage of the yarn through thedetection area of the yarn sensor 6 exceeds a time threshold. If thiscondition is not fulfilled, the microprocessor continues with programmestep No. 22, whereas if it is not fulfilled, it goes to programme stepNo. 25.

At programme step No. 25, the weaving machine is stopped since a yarnbreakage has occurred. For this purpose, the microprocessor 20 generatesa "high" potential on the output pin P51 of the first expansion circuit38.

At programme step No. 26, the microprocessor 20 goes back to thestart-instruction of the programme when having received a reset-signal.

At programme step No. 27, the microprocessor 20 actuates the stoppingdevice as determined or selected during programme step No. 3 forstopping the yarn withdrawal from the storage drum 2. Furthermore, themicroprocessor 20 stores the number of the now actuated stopping devicein a pedetermined storage cell of its RAM.

At programme step No. 28, the microprocessor 20 checks whether thetrigg-signal as received at programme step No. 6 has disappeared in themeantime. As soon as the trigg-signal has disappeared, themicroprocessor 20 goes to programme step No. 29.

At programme step No. 29, the microprocessor 20 carries out a programmestep corresponding to programme step No. 2.

At programme step No. 30, the microprocessor 20 carries out a programmestep corresponding to programme step No. 3.

At programme step No. 31 there is a waiting routine for repeatedlychecking whether a trigg-signal is fed to the trigg-input 32. Such atrigg-signal indicates that the weaving machine is ready for theinsertion of a weft yarn again. As soon as the trigg-signal isgenerated, the microprocessor 20 goes to programme step No. 32.

At programme step No. 32, the microprocessor 20 switches on the main airjet nozzle of the weaving machine by generating a "high" potentialsignal at output pin P50 of the first expansion circuit 38.

At programme step No. 33, the microprocessor 20 de-actuates the stoppingdevice actuated when carrying out the programme step No. 27. Themicroprocessor then goes back to programme step No. 13.

The present invention is not limited to the embodiment described in theabove and shown in the drawings, but several other embodiments arepossible within the scope of the invention.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. An apparatus forcontrolling a plurality of relay nozzles in a jet weaving machine,comprising control means for consecutively actuating said nozzles forsupporting the insertion of a weft yarn into the shed of the weavingmachine and up to the arrival end of said shed by consecutively openingsolenoid valves associated with said nozzles, said valves beingcontrolled on the basis of calculated information representing themomentary real position of the weft yarn during its movement through theshed, said weaving machine including a yarn storing, feeding andmeasuring device for the weft yarn to be supplied, said device includinga stationary storage drum onto which an intermediate yarn store is woundby a winding-on member and from which the yarn is withdrawn spirallingaround a withdrawal end of the storage drum, yarn sensing means arrangedsuch that the weft yarn periodically passes its detection area duringwithdrawal from the drum, said yarn sensing means producing pulsesignals, each said pulse signal indicating that the yarn is passing itsdetection area, and at least one yarn stopping device located at thewithdrawal end of the storage drum and including a yarn stopping elementand actuator means for moving said stopping element into and out of thepath of the yarn being withdrawn, said control means including anactuator control device which has storing means for storing informationregarding the yarn stopping device actuated at the end of the nextpreceding yarn withdrawal cycle and has calculating means fordetermining the momentary position of the withdrawal point of the yarnbased on said stored information and on the periods of time betweensuccessive pulse signals from the yarn sensing means, said calculatingmeans being electrically connected to said solenoid valves of the relaynozzles, and said calculating means transmitting a respective actuationsignal to each of said nozzles for opening said nozzle at the momentwhen the calculated momentary position of the withdrawal point of theyarn on the storage drum corresponds to a length of the weft yarn beingwithdrawn which is equal to the distance of said nozzle from theinsertion end of the shed of the weaving machine.
 2. Apparatus asclaimed in claim 1, wherein said calculating means includes positiondetermining means for determining the momentary position of thewithdrawal point of the weft yarn, said position determining meansincluding means for:(a) setting the calculated momentary position to avalue corresponding to the position of the previously actuated yarnstopping device,(b) incrementing the calculated momentary position at apredetermined rate and checking whether the calculated momentaryposition equals the position of the yarn sensing means, and (c) when thecalculated position is equal to the position of the yarn sensing means,holding the calculated momentary position while awaiting a pulse signalfrom the yarn sensing means and going back to step (b) as soon as theyarn sensing means generates said pulse signal, the generation of saidpulse signal indicating that the calculated momentary position is equalto the real position of the withdrawal point of the yarn.
 3. Apparatusas claimed in claim 1, wherein the yarn sensing means has only onesingle yarn sensor.
 4. Apparatus as claimed in claim 1, wherein saidcalculating means includes a microprocessor.
 5. Method for controlling ajet weaving machine which includes a yarn storing device from which aweft yarn can be withdrawn and a plurality of selectively actuable relaynozzles provided at spaced locations along a shed of the weaving machineto carry a weft yarn withdrawn from said storing device through theshed, comprising the steps of: monitoring the speed at which a weft yarnis withdrawn from said storing device; periodically calculating themomentary position of the weft yarn being inserted through the shed as afunction of the actual speed of withdrawal of the weft yarn from thestoring device; and successively actuating said relay nozzles during theinsertion of the weft yarn through the shed by generating a respectiveactuation signal for each said relay nozzle when said calculatedmomentary position reaches a respective predetermined value associatedwith such relay nozzle.
 6. Method for controlling a plurality of relaynozzles in a jet weaving machine having a yarn storing, feeding andmeasuring device, stopping means for preventing withdrawal of a yarnfrom said yarn storing, feeding and measuring device, and yarn sensormeans located close to the path of the yarn for detecting the withdrawalof the yarn from a storage drum of said yarn storing, feeding andmeasuring device, said relay nozzles being consecutively actuated forguiding and supporting the weft yarn through a shed of the fabric afterdeactuating said stopping means, comprising the steps of:continuouslymeasuring the period of time elapsed following a deactuation of saidstopping device for initiating a weft yarn insertion; periodicallycalculating an actual withdrawal length of said yarn on the basis ofsaid measured period of time, and correcting said calculated withdrawallength on the basis of a signal generated by said yarn sensor means; andsuccessively actuating the respective relay nozzles on the basis of saidcorrected calculated withdrawal lengths.
 7. Method as claimed in claim6, wherein the step of correcting said calculated withdrawal lengthincludes the step of measuring the period of time between consecutivepulse signals generated by said yarn sensor.
 8. Apparatus forcontrolling a jet weaving machine which includes a yarn storing devicefrom which a weft yarn can be withdrawn and a plurality of selectivelyactuable relay nozzles provided at spaced locations along a shed of theweaving machine to carry through the shed a weft yarn withdrawn from thestoring device, comprising sensor means in the region of said storingdevice for monitoring the speed at which a weft yarn is withdrawn fromsaid storing device, and calculating means responsive to said sensormeans for peridically calculating the momentary position of the weftyarn being inserted through the shed as a function of the actual speedof withdrawal of the weft yarn from the storing device and forsuccessively actuating said relay nozzles by generating a respectiveactuation signal for each said relay nozzle when said calculatedmomentary position reaches a respective predetermined value associatedwith such relay nozzle.
 9. Apparatus for controlling relay nozzles in ajet weaving machine, comprising: a yarn storing, feeding and measuringdevice for the weft yarn to be supplied, said yarn storing, feeding andmeasuring device including a storage drum; yarn sensing means arrangedso that the weft yarn periodically passes its detection region duringwithdrawal from the drum, said sensing means producing a pulse each timethe yarn passes its detection region; at least one yarn stopping devicewhich is located at the withdrawal end of the storage drum and which,when actuated, prevents withdrawal of the yarn from said drum; andcalculating means for periodically calculating the momentary withdrawallength of the yarn on the basis of the periods of time betweenconsecutive pulse signals from said yarn sensing means, wherein saidcalculating means is electrically connected to said relay nozzles andtransmits a respective actuation signal to each said nozzle as soon asthe momentary withdrawal length of the yarn is equal to the distance ofsuch nozzle from an insertion end of the shed of the weaving machine.10. Apparatus as claimed in claim 9, including at least two of said yarnstopping devices, wherein said calculating means further includesstoring means for storing information identifying the yarn stoppingdevice actuated at the end of an immediately preceding yarn withdrawalcycle, and wherein said calculating means calculates the momentarywithdrawal length of the yarn on the basis of said stored informationand on the basis of the periods of time between consecutive pulsesignals received from said yarn sensing means.
 11. Apparatus as claimedin claim 10, wherein said calculating means includes means for:(a)setting the calculated momentary position to a value corresponding tothe position of the previously actuated yarn stopping device; (b)incrementing the calculated momentary position at a predetermined rateand checking whether the calculated momentary position is equal to theposition of said yarn sensor means; and (c) when the calculatedmomentary position equals the position of the yarn sensor means, holdingthe calculated momentary position while awaiting a pulse generated bysaid yarn sensor means and going back to step (b) as soon as said yarnsensor means generates a pulse, wherein the generation of a pulse bysaid yarn sensor means indicates that the calculated momentary positionequals the real position of the withdrawal point of the yarn. 12.Apparatus as claimed in claim 9, wherein the yarn sensing means has onlya single yarn sensor.
 13. Apparatus as claimed in claim 9, wherein saidcalculating means includes a microprocessor.